vga print helpers
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pantonshire committed
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@@ -37,17 +37,17 @@ self_load:
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; Panic if the partition / boot1 starting LBA overflows 16 bits.
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or ebx, ebx
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jnz panic
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jnz panic_simple
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ror eax, 16
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or ax, ax
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jnz panic
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jnz panic_simple
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ror eax, 16
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; Calculate the boot1 end LBA and panic if it overflows 16 bits.
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; n.b. ebx is zero before this so both bx and ebx can be used as the boot1 end LBA.
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mov bx, ax
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add bx, BOOT1_TOTAL_SECTORS
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jc panic
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jc panic_simple
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; Panic if the boot1 end LBA is after the partition end LBA.
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; If the upper 32 bits of the partition end LBA are nonzero, then it must be greater than our
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@@ -56,7 +56,7 @@ self_load:
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jnz .end_lba_ok
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; Compare the boot1 end LBA to the lower 32 bits of the partition end LBA.
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cmp ebx, ecx
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ja panic
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ja panic_simple
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.end_lba_ok:
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@@ -74,7 +74,7 @@ self_load:
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mov ecx, ebx
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call read_sector
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jc panic
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jc panic_simple
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add ebx, 512
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inc word [bp - 0x02]
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@@ -82,32 +82,15 @@ self_load:
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.self_load_done:
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mov ebx, cafebabe
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; Check the magic bytes at the end of boot1.
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push es
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mov ebx, boot1_magic
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call addr32_to_addr16
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mov eax, es:[ebx]
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hlt
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cmp dword es:[bx], BOOT1_MAGIC
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pop es
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jne panic_simple
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call test_a20
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add al, 0x30
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mov byte fs:[0x0000], al
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hlt
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pr_womble:
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; Reveal the true nature of jen
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xor bx, bx
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.loop:
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cmp bx, WOMBLE_LEN
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jae .done
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lea si, [womble + bx]
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mov dh, [si]
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mov di, bx
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shl di, 1
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mov byte fs:[di], dh
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mov byte fs:[di + 0x01], 0x1f
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inc bx
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jmp .loop
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.done:
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hlt
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jmp main
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; Converts a 32-bit address to a 16-bit sector and offset.
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@@ -119,8 +102,7 @@ pr_womble:
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; - cf: unset on success, set on failure
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; Clobber: none
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addr32_to_addr16:
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push bp
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mov bp, sp
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fnstart
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push es
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push eax
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@@ -152,9 +134,8 @@ addr32_to_addr16:
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.fail:
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pop eax
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pop es
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pop bp
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stc
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ret
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fnret
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; Reads a single sector at the given LBA into memory.
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@@ -170,8 +151,7 @@ read_sector:
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; head = temp % n_heads
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; cylinder = temp / n_heads
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push bp
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mov bp, sp
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fnstart
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push es
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push ebx
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@@ -203,8 +183,14 @@ read_sector:
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.return:
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pop ebx
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pop es
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pop bp
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ret
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fnret
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panic_simple:
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mov ax, 0x0003
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int 0x10
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mov word fs:[0x0000], 0x4f21
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hlt
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%if ($ - $$) > 512
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@@ -212,7 +198,183 @@ read_sector:
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%endif
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main:
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; Set VGA mode
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; https://mendelson.org/wpdos/videomodes.txt
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mov ax, 0x0003
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int 0x10
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; Disable the cursor (don't want to look at the blink blink blink)
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mov ax, 0x0100
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mov cx, 0x3f00
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int 0x10
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mov word [GLOBALS + VGA_COL], 0x1f00
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call vga_clear
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mov ax, msg_boot1_loaded
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mov cx, MSG_BOOT1_LOADED_LEN
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call vga_println
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call test_a20
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test ax, ax
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jnz .a20_enabled
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mov ax, msg_a20_disabled
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mov cx, MSG_A20_DISABLED_LEN
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call vga_println
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; TODO: enable a20
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hlt
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.a20_enabled
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mov ax, msg_a20_enabled
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mov cx, MSG_A20_ENABLED_LEN
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call vga_println
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hlt
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; Clear the VGA text buffer.
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; Arguments: none
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; Return: none
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; Clobber: none
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vga_clear:
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fnstart
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push di
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push es
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push ax
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push cx
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mov ax, 0xb800
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mov es, ax
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mov ax, [GLOBALS + VGA_COL]
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mov cx, VGA_WIDTH * VGA_HEIGHT
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xor di, di
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rep stosw
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mov word [GLOBALS + TEXTBUF_LINE], 0
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pop cx
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pop ax
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pop es
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pop di
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fnret
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; Scroll the VGA text buffer up one line.
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; Arguments: none
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; Return: none
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; Clobber: none
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vga_scroll:
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fnstart
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push si
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push di
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push ax
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push cx
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push es
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push ds
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mov ax, 0xb800
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mov ds, ax
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mov es, ax
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; Copy everything up one line.
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mov cx, VGA_WIDTH * (VGA_HEIGHT - 1)
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mov si, VGA_WIDTH * 2
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mov di, 0
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rep movsw
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; Clear the last line.
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mov ax, [GLOBALS + VGA_COL]
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mov cx, VGA_WIDTH
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mov di, VGA_WIDTH * (VGA_HEIGHT - 1) * 2
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rep stosw
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pop ds
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pop es
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; Decrement the current textbuf line if it's greater than 0.
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mov cx, [GLOBALS + TEXTBUF_LINE]
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xor ax, ax
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sub cx, 1
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cmovae ax, cx
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mov [GLOBALS + TEXTBUF_LINE], ax
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pop cx
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pop ax
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pop di
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pop si
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fnret
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; Write one line to the VGA text buffer.
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; Arguments:
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; - ax: pointer to the string to print
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; - cx: string length
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; Return: none
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; Clobber: ax, cx
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vga_println:
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fnstart
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push si
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push di
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push dx
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push es
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cmp word [GLOBALS + TEXTBUF_LINE], VGA_HEIGHT
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jb .scroll_done
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call vga_scroll
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.scroll_done:
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mov si, ax
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mov ax, VGA_WIDTH
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cmp cx, ax
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cmova cx, ax
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mov di, VGA_WIDTH * (VGA_HEIGHT - 1) * 2
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xor dx, dx
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mov ax, [GLOBALS + TEXTBUF_LINE]
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mov di, VGA_WIDTH * 2
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mul di
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mov di, ax
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mov ax, 0xb800
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mov es, ax
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mov ah, [GLOBALS + VGA_COL + 1]
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.loop:
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or cx, cx
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jz .done
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mov al, [si]
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mov es:[di], ax
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add di, 2
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inc si
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dec cx
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jmp .loop
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.done:
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inc word [GLOBALS + TEXTBUF_LINE]
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pop es
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pop dx
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pop di
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pop si
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fnret
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enable_a20:
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fnstart
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fnret
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; Check whether the A20 line is enabled. Writes to the boot sector identifier.
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; Arguments: none
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; Return:
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; - ax: 0 if A20 disabled, nonzero if A20 enabled
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; Clobber: none
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test_a20:
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push bp
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mov bp, sp
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push gs
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; Restore the boot sector identifier in case it was overwritten by anything.
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@@ -238,22 +400,20 @@ test_a20:
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.return:
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pop gs
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pop bp
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ret
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panic:
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mov ax, 0x0003
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int 0x10
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mov word fs:[0x0000], 0x4f21
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hlt
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msg_boot1_loaded db "boot1 loaded. hello!"
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MSG_BOOT1_LOADED_LEN equ $ - msg_boot1_loaded
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msg_a20_enabled db "a20 enabled"
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MSG_A20_ENABLED_LEN equ $ - msg_a20_enabled
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msg_a20_disabled db "a20 disabled"
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MSG_A20_DISABLED_LEN equ $ - msg_a20_disabled
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msg_panic db "fuck"
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MSG_PANIC_LEN equ $ - msg_panic
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womble db "jen is a womble!"
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WOMBLE_LEN equ $ - womble
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times 409600 db 0
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cafebabe:
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dd 0xfeedface
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boot1_magic dd BOOT1_MAGIC
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BOOT1_TOTAL_LEN equ $ - $$
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BOOT1_TOTAL_SECTORS equ (BOOT1_TOTAL_LEN + 511) / 512
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@@ -6,6 +6,11 @@
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%define EBDA_START 0x080000
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%define BOOT1_MAGIC 0x544e4150
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%define VGA_WIDTH 80
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%define VGA_HEIGHT 25
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; boot0 base stack frame variable offsets / globals
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; (we use the same offsets once we copy the variables to the globals section)
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; -------------------------------------------------------------------------------------------------
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@@ -29,3 +34,18 @@
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%define GPT_SECTORS_LOADED 0x16
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%define GPT_CURRENT_LBA 0x18
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%define BOOT1_GPT_ENTRY_ADDR 0x1a
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; Globals
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; ------------------------------------------------------------------------------------------------
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%define VGA_COL 0x1c
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%define TEXTBUF_LINE 0x1e
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%macro fnstart 0
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push bp
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mov bp, sp
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%endmacro
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%macro fnret 0
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pop bp
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ret
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%endmacro
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